Fibroblasts will be cultured from the papillary, reticular and subcutaneous fat layers of normal and scleroderma skin. Primary cultures and subcultures will receive a 24-hour pulse with 3H-proline and subjected to the following determination: (a) proline and hydroxyproline following hydrolysis and amino acid analysis, (b) limited pepsin digestion, (c) separation of pepsin-resistant labelled material by discontinuous SDS-acrylamide gel electrophoresis, and (d) Agarose A5 chromatography to estimate type I/type III collagen ratios. Pro-collagen type III and fibronectin will be estimated by radioimmunoassay. Immunoelectron microscopy of normal and sclerodermal skin will be performed with specific antibodies against type I collagen and pro-collagen, type III collagen and pro-collagen, and fibronectin.